1. Field of the Invention
The present invention relates to a phase change material that couples an integrated circuit package to a thermal element.
2. Background Information
FIG. 1 shows an electronic assembly 1 of the prior art. The assembly 1 includes a first integrated circuit package 2 and a second integrated circuit package 3 that are mounted to a substrate 4. The substrate 4 may be a printed circuit board such as a motherboard, or the circuit board of a cartridge that can be plugged into a motherboard. The first integrated circuit package 2 may contain an integrated circuit (not shown) such as a microprocessor. The second integrated circuit package 3 may contain a memory device such as a static random access memory (SRAM) integrated circuit.
The integrated circuits generate heat that must be removed from the packages. A thermal element 5 may be coupled to the packages to facilitate the removal of the heat. The thermal element 5 may be an aluminum or copper plate that is attached to the substrate 4 and coupled to the top surfaces of the packages 2 and 3. Heat flows through the packages 2 and 3 and into the thermal element 5. The thermal element 5 increases the effective surface area and the resultant heat transfer into the ambient.
The first integrated circuit package 2 may have a height that is greater than the second integrated circuit package 3. The difference in height may create an air gap between the thermal element 5 and the second package 3. Additionally, tolerances in the assembly 1 may also create air gaps between the thermal element 5 and both packages 2 and 3.
Air gaps increase the thermal impedance between the thermal element 5 and the packages 2 and 3. The higher impedance increases the junction temperatures of the integrated circuits. The air gaps may be filled with thermal grease 6 located between the thermal element 5 and the packages 2 and 3. The grease 6 is typically applied to the thermal element 5, or integrated circuit packages 2 and 3, before the element 5 is assembled onto the packages 2 and 3.
The thermal grease 6 has a thermal conductivity that is greater than the thermal conductivity of air. The thermal grease is compliant enough to compensate for variations in the thickness of each air gap. Unfortunately, it has been found that thermal grease may pump or bleed out of the space between the thermal element 5 and packages 2 and 3 and leave an air gap. It would be desirable to provide a compliant thermally conductive material that can couple the thermal element to the packages and will not bleed out of the package/element interface during the life of the assembly.